Ammonia is an extremely important chemical which has innumerable uses in a wide range of areas, for example: process, industry and utility uses. The instant invention is concerned with a method and means to safely produce relatively small amounts (i.e. up to 150 pounds per hour, and perhaps up to 300 pounds per hour) of ammonia from urea, for such uses.
Areas of use for such relatively small quantities of ammonia are quite varied and, for purposes of this discussion, such areas include, but are not limited to: providing ammonia equipment and processes, of the type illustrated in U.S. Pat. No. 2,356,717, to help increase the efficiency of an electrostatic precipitator to remove flyash from the flue gas stream of a fossil fuel burning boiler; to alleviate “blue plume” problems when burning a high sulfur content oil in a boiler such as illustrated in U.S. Pat. No. 5,024,171; and to remove the NOx contaminants contained in a flue gas stream of energy producing boilers or combined cycle systems, in conjunction with selective catalytic reduction (SCR), and/or selective non-catalytic reduction (SNCR), systems (see U.S. Pat. Nos. 4,124,536 and 3,900,554, respectively).
Ammonia for uses such as described above, is often delivered in the form of anhydrous ammonia, or aqueous ammonia. Anhydrous ammonia is used in massive quantities world-wide for many industrial and agricultural purposes. Anhydrous ammonia is gas at ambient temperatures and pressures, and is normally shipped and stored as a liquid, either in pressure vessels at ambient temperature, and high pressure (i.e. over 16 bars ), or in refrigerated vessels at ambient or nearly ambient pressure, and at about −33° C. It is transported in bulk in ships, barges, and railroad tank cars, and in tank trucks on public roads and highways and, in instances of relatively small usage per hour, such as envisioned with the present invention, perhaps in high pressure cylinders. It is frequently used and stored at industrial sites in populated areas. It is now coming into wider use for the removal of NOx from flue gas at power generating stations, industrial heaters, or in combined cycle systems, in urban areas.
Anhydrous ammonia is an extremely hazardous, toxic, and volatile material. In the event of an accidental discharge, it can cause immediate death or injury to humans and animals and rapid death to trees and plants. Both anhydrous liquid ammonia, and concentrated aqueous liquid ammonia, display a deadly characteristic which substantially increases the risk of widespread injury and death in case of a spill. Specifically, upon sudden release to the atmosphere, as might occur in a sudden and accidental discharge, the ammonia can form a cloud produced of an aerosol fog of liquid ammonia droplets. Unlike gaseous ammonia, which, though toxic, is lighter than air and quickly dissipates to harmless concentrations, the cloud can persist for a surprisingly long time, as long as several hours, before it finally disappears. The cloud is typically heavier than air and tends to drift along the surface of the earth, i.e., the ground or the surface of a body of water. The cloud moves with the wind and can sweep over a total area, i.e., a “footprint,” much larger than the area covered by the cloud at any one moment. Contact with the cloud may be instantly incapacitating, and a single breath can be fatal.
In addition to the inherent danger of storing, transporting and handling large quantities of ammonia, the expense insofar as safety aspects, insurance costs, specialized training, and the difficult to quantify emotional exposure of living and/or working next to a such potential catastrophe, it is apparent that if another, less hazardous commodity could be transported or stored instead of ammonia, and then be readily converted to ammonia, the hazards associated with ammonia shipment and handling would be considerably reduced. To some extent, attempts have been made in the supply of ammonia for NOx control in power plant and industrial environments by substituting concentrated aqueous liquid ammonia for anhydrous ammonia. Such a solution has achieved only limited success, due to any number of factors, for example: the high energy cost of transporting and vaporizing the water carrier, relatively costly storage facilities; and, even though aqueous ammonia is safer to handle than anhydrous ammonia, it is still difficult and costly to handle in a safe manner.
Urea is an ideal candidate as an ammonia substitute. Urea is a non-toxic chemical compound and, for purposes of this discussion, presents essentially no danger to the environment, animals, plant life and human beings. It is solid under ambient temperatures and pressures. Consequently, urea can be safely and inexpensively shipped in bulk and stored for long periods of time until it is converted into ammonia. It will not leak, explode, be a source of toxic fumes, require pressurization, increase insurance premiums, require extensive safety programs, or be a concern to the plant, community and individuals who may be aware of the transportation and/or storage dangers of ammonia. Further, urea can be used to produce gaseous ammonia:                on-site        on-demand        with rapid response time        with maximum turn down availability        with utmost safety        with significant economies        with automatic operation        with low maintenance        
The use of urea with the advantages discussed hereinabove were recognized by Applicant heretofore, as illustrated, described and claimed in his U.S. Pat. No. 6,093,380. In addition to the system described in the '380 Patent, another commercially available system which also produces ammonia form a urea feed stock is shown in U.S. Pat. No. 6,077,491 The prior art systems mentioned in this paragraph have been used primarily for fulfilling relatively larger ammonia requirements and, as such, are not necessarily the most appropriate design for small ammonia production requirements. For example—cost, unnecessarily high pressure and temperature requirements, speciality metals, physical and chemical scale down problems, load following requirements, expensive or ineffective controls for such small ammonia production requirements, and the like.